MORTGAGE LOANS (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2013 item	Sep. 30, 2013 item	Dec. 31, 2012
Mortgage loans
Mortgage loan holdings	$ 4,794,924,000	$ 4,794,924,000	$ 4,948,625,000
Amount that would become due in 2013, if loans are called at their next call dates	66,400,000	66,400,000
Amount that would become due in 2014 through 2018, if loans are called at their next call dates	1,200,000,000	1,200,000,000
Amount that would become due in 2019 through 2023, if loans are called at their next call dates	575,000,000	575,000,000
Amount that would become due after 2023, if loans are called at their next call dates	174,400,000	174,400,000
Allowance for loan and credit losses	8,000,000	8,000,000	2,900,000
Change in the allowance for credit losses
Ending balance	8,000,000	8,000,000	2,900,000
Commercial mortgage loans
Mortgage loans
Mortgage loan holdings	4,800,000,000	4,800,000,000
Allowance for loan and credit losses	7,970,000	7,970,000	2,875,000
Mortgage loans having participation feature	714,500,000	714,500,000	817,300,000
Income recognized on participating mortgage loans	3,700,000	12,900,000
Nonperforming mortgage loans, foreclosed properties and restructured loans pursuant to pooling and servicing agreement	16,400,000	16,400,000
Nonperforming mortgage loans, foreclosed properties and restructured loans to invested assets (as a percent)	0.05%	0.05%
Number of mortgage loans accounted for as troubled debt restructurings	2
Principal balance of loan	3,200,000	3,200,000
Reserves related to restructuring	0	0
Number of loan categories		2
Nonperforming or restructured loans not subject to a pooling and servicing agreement	10,700,000	10,700,000
Number of nonperforming loans not subject to a pooling and servicing agreement which have been restructured		2
Loans subject to a pooling and servicing agreement which are nonperforming	5,700,000	5,700,000
Number of nonperforming loans subject to a pooling and servicing agreement which have been restructured		0
Change in the allowance for credit losses
Beginning balance		2,875,000	4,975,000
Charge offs		(2,643,000)	(8,340,000)
Recoveries		(374,000)	(628,000)
Provision		8,112,000	6,868,000
Ending balance	$ 7,970,000	$ 7,970,000	$ 2,875,000
Commercial mortgage loans | Minimum
Mortgage loans
Period for exercise of call options or interest rate reset options		3 years
Commercial mortgage loans | Maximum
Mortgage loans
Period for exercise of call options or interest rate reset options		10 years
Loan-to-value ratio with participating interest (as a percent)	85.00%	85.00%